The invention relates to fuel cells. More particularly, the invention relates to fuel cell catalyst electrodes. Even more particularly, the invention relates to methods of cleaning such catalyst electrodes.
Polymer electrolyte fuel cells (PEFCs), including direct methanol fuel cells (DMFCs), have attracted great interest as an alternative power source for vehicles and portable electronic devices. Two major challenges facing PEFCs are the reduction of material costs and the need for improved performance. Regarding the former challenge, non-platinum catalysts based on metals such as ruthenium, palladium, iron, manganese, cobalt nickel, chromium, molybdenum, and vanadium have been investigated.
Regarding the latter challenge, it has been recognized that the presence of some metallic oxides tend to contaminate cathode catalyst layers, leading to a decrease in oxygen reduction reaction (ORR) activity in such cathodes and a corresponding reduction in fuel cell performance. In some instances, metallic species may migrate from one electrode to the other under fuel cell operating conditions and in the presence of a contaminated oxidation/reduction catalyst.
Methods of removing such contaminants have included treatment of the catalytic electrode material with acids ranging from organic carboxylic acids to dilute sulfuric acid. Such treatment appears to yield varying results: the process is either incomplete, if mild treatment conditions are used, or results in significant loss of metal if conditions are too harsh.
While oxide contaminants on fuel cell electrodes adversely affect fuel cell performance, methods of removing such materials are highly variable and may result in loss of electrode material. Therefore, what is needed is a method of removing such contaminants from a fuel cell catalyst material. What is also needed is a method of removing such contaminants in situ from a membrane electrode assembly. In addition, what is needed is a method of improving fuel cell performance based on the removal of such contaminants.